The present invention relates to a display element and plasma display panel preferably used for an image display of a television or computer.
A conventional AC plasma display panel is illustrated in part in FIG. 5. As shown in FIG. 5, a plurality of scanning electrodes 4 and sustaining electrodes 5 that are parallel to each other are formed on a first insulative substrate 1. The scanning electrodes 4 and the sustaining electrode 5 are covered with a dielectric layer 2 and a protective layer 3. On a second insulative substrate 6, which faces the first insulative substrate 1, a plurality of data electrodes 7 that are parallel to each other are formed orthogonally to the scanning electrodes 4 and the sustaining electrodes 5. The data electrodes 7 are covered with a base glass layer 8 made of white material. A plurality of ribs 9 also made of white material are formed on the base glass layer 8. The ribs 9 are arranged so that each cooperates with a neighboring rib to define a channel adjacent to and along a data electrode 7. A phosphor 10 is provided in each channel to cover opposing side walls of the neighboring ribs, and a part of the base glass layer is exposed between the neighboring ribs, so that a discharge chamber 11 is defined on and along a phosphor 10.
As can be seen in the drawing, the neighboring scanning and sustaining electrodes, 4 and 5, are paired so that an electric discharge can be produced with aid of the data electrode 7 in a restricted region of the discharge chamber 11. The electric discharge generates ultraviolet light that excites an adjacent part of a phosphor 10. The excited portion of the phosphor 10 emits visible light for displaying an image. In this manner, each area where a data electrode 7 crosses a pair of scanning and sustaining electrodes, 4 and 5, defines a discharge cell 12 as hatched in FIG. 5.
As shown in the drawing, three neighboring phosphors 10, each separated by the ribs 9, constitute a red phosphor 10R, a green phosphor 10G, and a blue phosphor 10B, respectively, in this order. Selected and used for the white material of both the base glass layer 8 and ribs 9 is, for example, a white glass that is reflective of visible light. Preferably, a thickness of the base glass layer 8 is as small as possible to minimize a voltage for driving the data electrodes 7. For this reason, typically, the base glass layer has a thickness of about 10 to 15 micrometers. Also, a thickness of the ribs 9 is as small as possible to maximize an opening area of the discharge chamber 11. For this reason, typically, each of the ribs 9 has a thickness of about 20 to 60 micrometers.
Referring to FIG. 6 illustrating a cross sectional view taken along lines VIxe2x80x94VI in FIG. 5, descriptions will be made to functions of the base glass layer 8 and ribs 9. FIG. 6 shows that only the green phosphor 10G is excited for emitting green light. For clarity of the drawing and illustrative purpose, only a few light passes are illustrated in the drawing, which passes may not be depicted correctly from an optical standpoint.
As shown in the drawing, ultraviolet light generated by the discharge between the scanning and sustaining electrodes, 4 and 5, with aid of the data electrode 7 excites the green phosphor 10G. This causes the green phosphor 10G to emit green light to be projected through the first insulative substrate 1 as depicted by the arrows in FIG. 6, displaying a corresponding image. At this moment, part of the green light emitted from a surface of the green phosphor 10G is reflected toward surfaces of the base glass layer 8 and ribs 9 and then transmitted through the first substrate 1 for displaying. This is so because, the base glass layer 8 and the ribs 9 are made of white material, for example, white glass, which is reflective of visible light.
With this arrangement, a brightness of the display panel is increased to a certain extent. However, the white material can reflect only about 50 to 60 percent of the visible light. Beyond that, the structure does not improve the brightness of the panel much. In addition, the remaining 40 to 50 percent of the light is transmitted into the white material where it may be damped. Disadvantageously, several to several tens percent of the light can reflect from the white material, which may provide an adverse effect.
FIG. 7 is a graph illustrating a relationship between thickness of the phosphor and brightness of light from the display panel. In this graph, thickness-brightness characteristic curve A is for the base glass layer 8 and ribs 9 having reflectance of 60 percent, and curve B is for the base glass layer and ribs having reflectance of zero percent. This graph shows that if the thickness is lower than about 15 micrometers the brightness increases with the thickness due to the reflected light from the base glass layer 8 and the ribs 9, and if the thickness is greater than about 25 micrometers the brightness no longer increases much. This means that it is effective to increase the thickness of the phosphor for increasing the brightness of the panel.
Next, referring to FIG. 8 which is a cross sectional view taken along lines VIxe2x80x94VI in FIG. 5, another description will be made with regard to the adverse effect of the transmitted light from the base glass layer and ribs. FIG. 8 illustrates that the discharge cells 12 of the red and green phosphors, 10R and 10G, are excited to emit respective light, but the discharge cell 12 of the blue phosphor 10B is not excited. For clarity of the drawing and illustrative purpose, only a few light passes are illustrated in the drawing, which passes may not be depicted correctly from an optical standpoint.
In this instance, as shown by solid lines or arrows, the red and green visible light emitted from the surfaces of red and green phosphors, 10R and 10G, respectively, is transmitted through the first substrate 1 for display. Likewise, as shown by dotted lines or arrows, red and green visible light emitted into the interior of the elements is reflected by the surfaces of the base glass layer 8 and ribs 9, then transmitted through the elements and then transmitted through the first substrate 1 for display.
Contrary to this, as shown by phantom lines or arrows, the visible light transmitted from the red and green phosphors, 10R and 10G, is further transmitted from the base glass layer 8 and ribs 9. A portion of light transmitted from the base glass layer and ribs may travel through neighboring phosphors for different colors. In this instance, the display light from the red phosphor 10R can merge with that from the green phosphor 10G. This will degrade purity of respective colors. In addition, another portion of light transmitted from the base glass layer and ribs may travel through a portion of the first substrate 1 facing the discharge cell 12 that is not excited, which disadvantageously serves as an additional light for display. In this instance, green light from the green phosphor 10G is emitted through the discharge cell of blue phosphor 10B which is not excited, which is referred to as xe2x80x9chalationxe2x80x9d.
The above-described problems, i.e., degradation of color purity and halation, are common to the conventional plasma display panels irrelevant of the number of discharge cells or display colors from discharge cells.
Accordingly, a plasma display panel according to the present invention has spaced apart and parallel first and second substrates substrate. A base glass layer is provided on one surface of the second substrate confronting the first substrate. A plurality of spaced apart parallel ribs are positioned on the base glass layer and between the first and second substrates. Each rib defines a channel with a neighboring rib. A plurality of phosphors capable of emitting light are provided, each of which is positioned in a channel. In particular, the base glass layer and/or ribs are made of material that is substantially impermeable to and non-reflective of visible light. With this arrangement, due to the material being substantially impermeable to and non-reflective of visible light, color purity is improved and halation is reduced, thereby allowing a high quality image to be displayed.